(1) Field of the Invention
The present invention relates to a support assembly for a deformable sealing element of a downhole tool, a downhole tool having a deformable sealing element, and to a method of supporting a deformable sealing element of a downhole tool. In particular, but not exclusively, the present invention relates to a support assembly for a deformable sealing element of a downhole tool such as a packer or a bridge plug.
(2) Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98
As is well known in the oil and gas exploration and production industry, a wellbore is drilled from surface in order to gain access to subterranean hydrocarbon deposits (oil and gas). The wellbore is typically drilled to a first depth and then lined with a steel casing which is cemented in place, both to support the drilled rock formations, and to prevent unwanted fluid ingress/egress. The wellbore is then extended to a further depth and a smaller diameter casing is located in the extended section, passing through the wellbore to surface, and which is also cemented in place. This process is repeated as necessary until the wellbore has been extended to a desired depth. If required, a liner may be located in the final drilled section, the liner tied in to the deepest section of casing in the wellbore. The well is then completed, which involves carrying out various downhole procedures so that well fluids can be recovered to surface through production tubing located in the cased wellbore.
During the drilling and completion of a wellbore, it is frequently necessary to isolate and thus seal-off a portion of the wellbore. For example, the production tubing is typically located within and sealed relative to the casing/liner using a ‘packer’. Packers are also used in other downhole procedures, including intervention operations, where a remedial action is to be carried out downhole. Packers typically include a deformable sealing element which, when the packer is activated, are compressed axially, urging the sealing element radially outwardly into sealing abutment with an inner wall of the casing/liner.
Other types of downhole tools include similar deformable sealing elements. Typical such tools include ‘bridge plugs’ used to isolate part of a wellbore, and ‘straddles’ which may be required in circumstances where a tubing has corroded, leading to unwanted fluid ingress/egress. Where a tubing has corroded, a straddle including a pair of spaced deformable sealing elements is run downhole to straddle across the corroded section. A first such element is located uphole of the corroded section, and a second such sealing element downhole of the corroded section. In this fashion, when the straddle is activated, the sealing elements are both urged outwardly into sealing engagement with the inner wall of the tubing, to bridge across and isolate the corroded section, thereby preventing further unwanted fluid ingress/egress.
Typically, the deformable sealing elements of tools such as packers, bridge plugs, straddles and the like are of an elastomeric material which, when compressed axially, deform radially outwardly into abutment with the respective downhole tubing. If or when it is desired to remove the tools from the wellbore, the tool is actuated to release an applied compressive axial loading, moving the sealing element out of abutment with the tubing in question, so that the tool may be returned to surface.
However, loads applied to the sealing element when it is compressed and urged into abutment with the tubing can cause a permanent deformation of the sealing element, making it difficult to retract the element from abutment with the tubing, thereby hampering return of the tool to surface. Furthermore, the loads applied to the sealing elements can result in the sealing element extruding axially along the wellbore, reducing the sealing effect and potentially leading to seal failure.
In an effort to address these problems and deficiencies, it has become common practice to incorporate ‘garter’ springs into axial ends of the sealing elements. The garter springs offer a greater resistance to deformation than a main portion of the sealing element, to thereby support the ends of the sealing element, with the aim of preventing axial extrusion of the sealing element along the wellbore. Furthermore, the springs are configured so as to elastically recover following removal of a deformation load, in an effort to assist retraction of the sealing element from abutment with the tubing.
Garter springs typically comprise an outer coil spring wound in a first direction, and an inner coil spring wound in the opposite direction and located within the outer coil spring. The garter springs are typically moulded into annular elastomeric sections of a harder, less compressible material than a main portion of the sealing element, which are bonded to the main portion. Moulding the garter springs into these annular sections, and bonding of the annular sections to the main portions, presents certain manufacturing difficulties.
Furthermore, the inner and outer coil springs are typically wound in opposite directions in an effort to prevent interengagement of coils of the springs following deformation of the sealing element, and the ingress of elastomeric material into the springs. However, it has been found that, in use and following deformation of the sealing element, the outer and inner coil springs nonetheless tend to become interengaged, and elastomeric material tends to penetrate the coils. This results in the garter springs becoming permanently deformed such that, when a deformation load applied to the sealing element is removed, the garter springs do not completely retract to their undeformed positions. This ultimately leads to a permanent deformation of the sealing element and the problems highlighted above. Also, this permanent deformation requires complete replacement of the sealing element before the tool can be reused.
It is amongst the objects of at least one embodiment of the present invention to obviate or mitigate at least one of the foregoing disadvantages.